Biography
A series introduces a character as sweet and lovable, a fountain of Heartwarming Moments, more comic relief than anything, who likes nothing more than to pet little creatures. They make you adore them, root for them, love them and want to hug them.
Then the writers proceed to slowly torment them in front of your very eyes. They destroy everything important to them, kill everyone they love and make them suffer from horrible accidents, diseases and acts of violence, including but not limited to torture, rape or any other Fate Worse than Death. They beat the character with one cruel stroke of fate after another until they are just an Empty Shell of their former cheerful, carefree self.
This technique is often used to build The Woobie in an attempt to enhance "adorability" points. Writers have to be careful or else The Cutie will become the universe's Chew Toy.
Be careful about torturing sweet little things — sometimes instead of breaking, or when there's nothing left to break, they snap. If they snap, you'd better hope your life insurance policy is up to date, especially if the cutie was a badass to begin with. If they break, but refuse to show it, they could be a Stepford Smiler.
Sometimes it can be Corrupt the Cutie, where the character in question breaks it by themself. Frequently a part of a character crossing the Despair Event Horizon or the cause of a Heroic BSoD. Also frequently part of the backstory of the Broken Bird, and instrumental in the Freudian Excuse of a villain who Used to Be a Sweet Kid. Compare Prone to Tears, who may have once undergone this, and Wide-Eyed Idealist. And sometimes this trope can straight-up kill the character in question.
On a more constructive note, sometimes breaking the cutie can result in a cute but weak character Taking a Level in Badass as they confront their tormentors and become more assertive. Circumstances may even lead to a cutie making an emotional recovery and regaining their sweet, hopeful nature. When the cutie refuses to break, they might become an iron or Stoic Woobie, a Determinator, or a Plucky Girl. If they are simply unbreakable to begin with, they are probably a Pollyanna.
Contrast Break the Haughty (where bad things happen to an arrogant person who had it coming), Break the Badass (when a super-strong person is put through the wringer), or the even worse variation, Kill the Cutie. Compare Break the Comedian, when the comedic relief gets made miserable. On the other hand, it may be possible to Heal the Cutie.